Document text
44 th International Conference on
Environmental Systems
TEXAS TECH
UNIVERSITY.
Visible-Light-Responsive Catalysts
Using Quantum-Dot Modified
Ti0 2 for Air and Water
Purification
University of
Central
Florida
Dr. Janelle L. Coutts
Dr. Paul E. Hintze
Dr. Christian A. Clausen
Mr. Jeffrey T. Richards
KSC, Engineering Services Contract
KSC, NASA NE-L Directorate
University of Central Florida, Dept, of Chemistry
KSC, Engineering Services Contract
Marriott University Park, Tucson, AZ
July 13-17, 2014
44 th International Conference on
Environmental Systems
Background & Project Goals
44 th International Conference on
Environmental Systems
Photocatalysis
■ Titanium dioxide has dominated
the field for decades
■ Commercially available Degussa
P25
■ 70-85% anatase, 15-30% rutile
■ 3.2 eV band gap for anatase requires
photons of 388 nm or lower (UV) for
activation
■ Traditional Hg-vapor light sources
precludes use in crewed spacecraft
■ Photonic energy requirements
disallow use of indoor lighting or
majority of solar spectrum
■ Only provides moderate reaction
rates
■ Somewhat low quantum yield
Processes occurring in a photocatalyst after electron-
hole separation (Agrios et al. 2003):
(a) Recombination of the electron and hole at the
surface
(b) Recombination of the electron and hole on the bulk
of the material
(c) Electron participation in the reduction reactions
(d) Hole participation in oxidation reactions
44 th International Conference on
Environmental Systems
Visible-Light-Activated Photocatalysis
■ Possible solution to photocatalysis limitations: enable Ti0 2 to become
visible light responsive (VLR)
■ Allows for use of better use of solar radiation (~45% of the spectrum lies in
the visible region)
■ Allows for use of highly efficient blue or white LEDs
■ Can lower electron-hole recombination events
■Applications include:
■ ISS applications
■ Air Trace Contaminant Control (TCC)
■ Water recovery systems
■ Low-cost H 2 production using solar energy
■ Enhanced chemical and microbial purification of water
How do we achieve this?
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44 th International Conference on
Environmental Systems
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44 th International Conference on
Environmental Systems
Project Goals
■ Development of a VLR-Ti0 2 catalyst library focused on coupling narrow
band gap semiconductors with Ti02 via:
■ Photodeposition
■ Mechanical alloying
■ Development of rapid screening methods in both aqueous and gas
phase for consistent evaluation of each catalyst
■ Comparison of catalysts prepared in-house and commercially available
VLR catalyst systems
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44 th International Conference on
Environmental Systems
Methods & Materials
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44 th International Conference on
Environmental Systems
Light Source Characterization
■ Custom light bank of six 24-W Marine Glo T5 high output fluorescent bulbs
utilized throughout this study
■ Irradiance profiles at varied distances determined in a dark room using an
Optronics Laboratories OL754C spectroradiometer
■ Sharp peaks at 404, 435, 546, 578 are due to emission lines from mercury
■ Broad peak from ~400 to 500 nm due to phosphor coating on the wall of the
lamp
■ Height with highest irradiance used for both aqueous and gas phase
studies
44 th International Conference on
Environmental Systems
Catalyst Preparation
■ 45 catalysts prepared by two methods: photodeposition or mechanical
alloying
■ Degussa P25 Ti0 2 coupled with metal sulfide quantum dots, metal selenide
quantum dots, and/or pure metal
■ Photodeposition formed quantum dots on Ti0 2 surface using UV radiation
and metal salts/sulfur quantum dot precursors
■ Mechanical alloying milled Ti0 2 with purchased quantum dots
Left: Photodeposition preparation
method for quantum dot
formation on Ti0 2
Right: Spex 8000M Mill used for
mechanical alloying
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Environmental Systems
Commerical VLR Catalyst
■GENS NANO Solution
■ Claims to allow treated surfaces
to be self-sanitizing and self-
cleaning
■ Proprietary altered Ti0 2 formula
that harvests solar or
fluorescent light energy to
activate catalyst
■ Sold as an aqueous sol solution
to be applied to surfaces
Deodorization Air Purification Sterilization
Wall, ceiling or other coated surface
purification
Decomposition by strong oxidative power
• Sterilizing
• Deodorizing
Photocatalytic Reaction
GENS NANO
SELF-SANITIZING
GREEN COATING
• Anti-bacterial & anti-mould
• Decontamination action 24/7 - 365 days/year
• Improvement of indoor air quality
• Natural mineral and water based
• Transparent, environmentally friendly
• CFIA Registered
TM
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44 th International Conference on
Environmental Systems
Rapid Aqueous Phase Assay
■ 4-chlorophenol (4CP) test contaminant
■ Catalyst loading rate: 10 mg/mL
contaminant solution
■ All reactions carried out in a Controlled
Environment Chamber (CEC) at 30°C
■ Dark adsorption for 30 min followed by
visible light irradiation for 30 min with
stirring
■ Analysis via HPLC for 4CP removal:
r> in/ CP] initial 1 nri
Removal % = r— — ; * 100
V [4 CP] Initia i I
Catalyst samples prepared for Liquid Assay
Liquid assay setup
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44 th International Conference on
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Rapid Gas Phase Assay
Gas assay setup
■ Ethanol test contaminant
■ 5 mg/mL aqueous catalyst slurry deposited on
aluminum coupons to create thin film
■Dark adsorption for 60 min followed by visible
light irradiation for 60 min
■ Analysis via GC-FID for ethanol removal and
acetaldehyde formation
■ Assay designed to be rapid; not optimized for
completed mineralization of EtOH to C0 2
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44 th International Conference on
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Catalyst Characterization
■ Diffuse Reflectance Analysis
■ Jasco V-670 UV/Vis spectrophotometer equipped with 60-mm diameter
integrating sphere
■ % reflectance from 300-800 nm
■ Reference material: Spectralon (Labsphere)
■ X-Ray Photoelectron Spectroscopy (XPS) Analysis
■ Thermo Scientific K-Alpha system
■ Completed for catalysts with appreciable VLR activity
■ Comparison for catalysts prepared via both methods
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Rapid Aqueous Phase Assay
1 5 catalysts with 0.4%+ per min degradation
rates of 4CP
1 Degussa P25 exhibited minute activity likely
due to small % of UV emitted from light
source
1 GENS NANO out performed by 2 in-house
catalysts
■ Other in-house catalysts showed near-
equivalent performance
Aqueous Phase Assay
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4CP removal capacity of top-performing
catalysts for aqueous phase assay.
PD = photodeposition method
MA = mechanical alloying method
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44 th International Conference on
Environmental Systems
Rapid Aqueous Phase Assay
1 Neither preparation method proved more
successful than the other in the current
experiment
1 Requires further investigation into
preparation method relationship with
catalyst activity
■ Mechanical alloying method, if determined to
be favored, is a faster process
■ Photodepositon followed by mechanical
alloying may further increase activity by
increasing catalyst surface area.
Comparison of Preparation Methods
Mech anicall y Alloy ed
Photodeposition
3 % Cu
1 % PbS
1 % CdS
3% CdS
Aqueous assay results with respect to
comparison method
16
ppm EtOH Oxidized to Products
44 th International Conference on
Environmental Systems
Rapid Gas Phase Assay
Gas Phase Assay
4CP removal capacity of top-performing
catalysts for gas phase assay.
PD = photodeposition method
MA = mechanical alloying method
■ 5 top-performing catalysts for
photocatalytic oxidation of ethanol to
acetaldehyde
■ Degussa P25 found to have ~18% removal
even with polyacrylic UV filter in place
■ 100% of UV exposure was not omitted
■ GENS NANO showed improvement over
bare Ti02 but not near the activity of in-
house catalysts
■ Acetaldehyde is not a favored product
■ Constraints on reactor design limited
analytical methods
■ Still serves as worthwhile indicator of
catalyst activity
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Rapid Gas Phase Assay
Comparison of Preparation Methods
Gas assay results with respect to
comparison method
■ Comparison of preparation methods shows
clear difference in activity
■ Photodeposition method proved superior to
mechanical alloying method
■ Could be due to oxidation of the metal
and/or quantum dot species during
mechanical alloying process
■ XPS analysis showed definitive differences
in metal and/or quantum dot peaks for the
alternate preparation methods
■ E.g.: PbS-modified sample showed intact PbS
peak for photodeposition method but was
altered in the mechanically alloyed sample
■ Shows drawback of high-energy, high-
temperature reactions
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44 th International Conference on
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Diffuse Reflectance Analysis
Diffuse Reflectance Spectra (Aq. Catalysts)
Diffuse Reflectance Spectra (Gas Catalysts)
Wavelength (nm)
Wavelength (nm)
Blank
Degussa P25
3% PbS (PD)
■ 3%Ag (PD)
0.3% PbS (PD)
0.1% PbS (PD)
1% Cu (MA)
■ Diffuse reflectance data allows for calculation of material's band gap energy
■ For all samples analyzed, there is a clear red-shift in the reflectance shoulder
■ Explains increased activity in visible region over Degussa P25
■ Degussa P25 shows two shoulders (anatase and rutile phase)
■ Several samples also exhibit multiple shoulders (Ti0 2 and other metal or quantum
dot)
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Conclusions & Future Work
■ Project Achievements:
■ Development of rapid assays for close the intellectual gap in current
research
■ Promising initial results for multiple in-house developed catalysts in both gas
and liquid phase assays
■ In-house catalysts with performance rates far above a commercially available
VLR catalyst
■ Further development can lead to many applications for ISS, future space
exploration systems, and terrestrially.
■ Results support a need for further investigation into top-performing
catalysts
■ Closer comparison of preparation methods
■ Optimization of catalysts
■ Further assays studying recalcitrant target compounds
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Acknowledgements
The authors would like to thank:
■ The late Dr. Lanfang Levine, KSC Engineering Services Contract
■ Dr. Steven Trigwell, KSC Engineering Services Contract
■ Lawrence Koss, KSC Engineering Services Contract
■ Dr. Thomas Graham, KSC NASA Postdoctoral Program
■ Dr. Phillip Maloney, KSC NASA Postdoctoral Program
Research support was provided by the Kennedy Space Center 2011
Center Innovation Fund (CIF)
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